Heat exchanger

A method of refrigerating a fluid, the method comprising:

• controlling (701) a flow of a refrigerant through an input tube fluidly connected to an inner space of a vessel through the input tube into an inner space and a flow of the refrigerant from the inner space into an output tube connected to the inner space, wherein the vessel comprises an inner wall and an outer wall, the inner wall and the outer wall are concentric and the inner space is bounded by at least the inner wall and the outer wall, an inlet and an outlet for transport of refrigerant into and out of the inner space, the outlet being adapted to be located above a highest level of the liquid refrigerant, and a tube inside the inner space arranged in a plurality of turns around the inner wall, that is adapted to be surrounded by the refrigerant and at least partly located within a bath of liquid refrigerant, the tube (631) is arranged to occupy at least two thirds of a volume of the inner space (607) with the plurality of turns being spaced apart from one another;
• controlling (702) a flow of a fluid to be refrigerated through the inner tube and
• controlling a pressure of the refrigerant in the inner space based on a target temperature of a fluid inside the tube.